<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <input type="text" name="" id="content" />
    <script>
      Element.prototype.eat = function () {
        console.log("eat food");
      };
      const input = document.getElementById("content"); // content = {}
      const body = document.body;
      const head = document.head;
      input.username = "jack";
      input.say = function () {
        console.log(this.username);
      };
      input.say();
      input.eat();
      body.eat();
      head.eat();
    </script>
  </body>
</html>
